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Answers to Thinking Critically Questions
Mader: Inquiry into Life, Twelfth Edition
Chapter 21
1. Compare the anatomy of the male and female reproductive tracts. Which organs serve
similar functions? Which organs serve a unique function, with no analogous function in the
other gender?
Explanation/Answer: Similar = testes and ovaries (produce gametes); epididymides and
oviducts (conduct gametes to location where fertilized); penis and vagina (organs of sexual
intercourse).
Unique = uterus (site for fetal development); male accessory organs (semen formation).
2. In the animal kingdom, only primates menstruate. Other mammals come into season, or
“heat,” during certain times of the year, while still others only ovulate after having sex.
What would be some possible advantages of a monthly menstrual cycle?
Explanation/Answer: Provides the opportunity to become pregnant each month. May save
energy by only preparing the uterus for a potential embryo for a short period each month.
The monthly sloughing of the endometrium may help to flush pathogens from the uterus.
3. Is it possible for some HIV-infected people to have relatively normal numbers of CD4+ T
cells in their blood (<500 per mm3), but still be in category C because they have one or more
AIDS-defining opportunistic infections? Why or why not?
Explanation/Answer: Their CD4+ T cells might not be functioning correctly, even though
the numbers haven’t changed. HIV may be affecting other aspects of their immune system
(macrophages, dendritic cells). They may have another, unrelated form of immunodeficiency
that already predisposes them to various opportunistic infections (HIV isn’t the only cause of
immunodeficiency!).
4. Suppose you have a friend who has HIV and has been on HAART for several years.
Recently she has begun to develop some opportunistic infections, and lab tests have shown
that her CD4+ T cell numbers are dropping, indicative that the HIV in her body is developing
resistance? Are there any possible options for her, or will she progress to full-blown AIDS
soon?
Explanation/Answer: Many different drug combinations can be used for HAART. She
could try a different combination, or perhaps could enroll in a trial of an experimental drug,
such as an integrase inhibitor. Sometime in this situation a patient will be instructed to stop
taking all antiretroviral drugs, to give her original, drug-sensitive virus a chance to bounce
back and compete with all the drug resistant strains. Then, the patient can be restarted on
HAART to inhibit the original, drug-sensitive virus.
5. The condition called benign prostatic hyperplasia is usually not life threatening, but prostate
cancer can be. Since the prostate gland is typically enlarged in both conditions, why is one
condition benign and the other potentially life threatening?
Explanation/Answer: Hyperplasia simply means an increase in size due to an increased
number of normal cells, whereas cancer implies a change in the type of cells involved. Some
cancers are actually benign, which means they don’t tend to metastasize or spread to other
organs, which can be life threatening.